An absorbent body for absorbent products such as disposable diapers, incontinence protectors and sanitary napkins is usually constructed of one or more layers of hydrophilic fibres, e.g. cellulose fluff. Furthermore, so-called superabsorbents are often included, which are polymers with the capacity to absorb many times their own weight in water or bodily fluid. Furthermore, additional components can sometimes be included in the absorbent body in order to improve, for example, its fluid spreading properties or to increase its coherence and ability to resist deformation during use.
A major problem, primarily in adult diapers and incontinence protectors intended to receive and absorb relatively large quantities of fluid, is that they often leak before their total absorbent capacity is completely used up. Since during urination, large quantities of fluid are often expelled during a few seconds, it is not uncommon that this results in the absorbent body being temporarily locally saturated with urine in the so-called fluid acquisition zone, when there is not enough time for the urine to be spread out to the other portions of the absorbent body and thus any more urine expelled will leak out of the diaper. Such early leakage is, of course, a great source of irritation for both the user and his caretaker. The leakage problem is accentuated upon repeated wetting.
Another problem is keeping the surface facing the user as dry as possible during the entire use and preventing so-called re-wetting, i.e. that already absorbed fluid is pressed back out of the absorbent body and wets the skin of the user or gives rise to leakage. To a certain extent, this re-wetting problems are alleviated if the absorbent body contains superabsorbents, which chemically bond the absorbed fluid even when the product has been subjected to external pressure, for example when the user sits down. One difficulty is, however, to design the absorbent body in such a way that the fluid is spread from the wetting area to unused portions of the absorbent body.
International patent application WO-A-9315702 describes an absorbent body comprising at least two different cellulose fluffs, the fibre structure in the first absorbent layer substantially consisting of a first type of fluff with an open fibre structure and low liquid dispersability, for example a cellulose fluff made chemo-thermal mechanically, and a fibre structure in the other absorbent layer essentially consisting of a second type of fluff with higher liquid dispersability than the fluff in the first absorbent layer, for example a chemically produced fluff. The first layer can, by virtue of its open fibre structure, house much liquid between the fibres and therefore can receive large amounts of liquid during a short period of time, i.e. it has a high momentaneous liquid absorbtion capacity. The other layer, which has a higher liquid dispersability than the first layer, is able to drain liquid from the first layer and spread it to the other layer.
EP-A-0,254,476 discloses an absorbent body, which in one zone essentially in front of the wetting area, has a lower surface weight and a lower density than the surrounding portions of the absorbent body. This provides an area with high momentaneous liquid absorption capacity, whereafter the liquid can be dispersed and stored in the surrounding areas of the absorbent body.
GB-A-2,082,643 describes an absorbent body with an essential uniform surface weight but with a density gradient in the longitudinal direction, so that the density increases towards the short sides of the absorbent body. This provides rapid liquid admittance in the central portion of the absorbent body out towards the more compressed end portions.
U.S. Pat. No. 4,413,996 describes an absorbent body for a diaper having a liquid absorbing depression or well in the wetting area. In this well, a porous batt can possibly be arranged.
There is, however, still room for improvement as regards liquid absorption capacity and dispersability, especially in products intended to be able to receive large quantities of liquid during a short period of time, which is often the case in, for example, incontintence products for adults. Another goal is that the surface of the absorbent body facing the user must be felt to be dry and comfortable, even after repeated wetting.